Zinc cyanide electrolyte



United States Patent Ofilice 2,757,134 Patented July 31, 1956 No Drawing. Application August 17, 1953, Serial No. 374,819

3 Claims. (Cl. 204-55) New Providence, N. J., assigno'r to East Pittsburgh,

This invention relates to the electrodeposition of zinc from electrolytes embodying certain brightening addition agents to promote zinc deposits of good quality and high ductility.

It is a general practice in the use of standard cyanide zinc plating solutions to add brightening agents thereto. Cyanide zinc plating solutions generally contain zinc cyanide, sodium cyanide and caustic soda. Before plating is begun with a standard solution of this type, a purifying agent is added thereto to assure precipitation of metallic contaminants such as lead, cadmium and tin. After the member has been plated with a desired thickness of zinc, it is usually given a bright dip in order to insure freedom from subsequent staining as well as to improve the brightness of the deposits.

An object of this invention is to provide an improved Zinc deposit from a cyanide zinc electroplating electrolyte by the addition of silver to the electrolyte.

A further object of this invention is to provide a brightening agent for cyanide zinc electroplating electrolytes which will operate to produce zinc deposits of good quality and high ductility with or without the conventional use of electrolyte purifying agents.

Also, an object of this invention is to provide a process for electroplating zinc from a cyanide zinc electrolyte using silver as a brightening agent.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

For a better understanding of the nature and objects of the invention, reference should be had to the following detailed description.

I have discovered that silver added to a cyanide zinc electrolyte will act as a brightening agent to provide electrodeposits of good quality and high ductility. With the addition of silver within critical limits, it is not necessary to use conventional purifying agents before plating from the electrolyte.

More particularly, the present invention is based on the addition of predetermined amounts of silver to a cyanide zinc electrolyte comprising as its essential ingredients zinc cyanide, sodium cyanide and caustic soda. The amount of silver required in the electrolyte to give effective brightening results is from 0.0005 to 0.5 ounce per gallon of electrolyte. The preferred range is from 0.001 to 0.01 ounce per gallon. The optimum silver concentration is about 0.005 ounce per gallon. The silver may be put in solution by dissolving any suitable silver compound therein, such as silver cyanide or silver oxide or from a silver anode.

The presence of the silver brightening agent promotes zinc deposits having a lustrous finish from cyanide zinc electrolytes in which there has been no purifying agent used.

With the use of conventional purifying agents admixed in the electrolyte, such as sodium sulfide or sodium polysulfide, zinc deposits of mirror bright finish are produced. It is necessary to maintain the concentration of silver in the electrolyte in an amount not exceeding 0.02 ounce .was plated on cathode per gallon, otherwise the silver would be precipitated by the purifying agent that may be optionally used.

Cyanide zinc electrolytes suitable for plating zinc are well known. A suitable cyanide zinc electrolyte widely used in-indu'stry at the present time is one containing from 8 to 10 ounces per gallon of zinc cyanide, from 3 to 5 ounces per gallon of sodium cyanide and from 8 to 12 ounces per gallon of caustic soda, the balance being water. The electrolyte is generally purified by the addition of from 0.05 to 0.1 ounce per gallon of sodium sulfide or from 0.03 to 0.06 ounce per gallon of sodium polysulfide. In using either sodium sulfide or sodium polysulfide, these sulfides are first completely dissolved in warm water and then stirred into the electrolyte by making small additions at numerous points along the plating tank.

Cyanide zinc electrolytes with silver as an addition agent may be employed for plating zinc by passing either continuous direct current or periodically reversed electrical current or other suitable electrical current therethrough. Excellent results have been obtained with direct current plating from such electrolytes. However, periodically reversed current has given electrodeposits characterized by the absence of nodules, and having smooth edges, smooth surfaces and a refined grain not attainable with direct current.

The following examples are illustrative of the practice of the invention:

Example I An aqueous electroplating electrolyte of. the following composition was prepared:

Ozs. per gallon Zinc Cyanide 8 Sodium Cyanide 5 Sodium Hydroxide 10.5 Silver 0.005

This bath was operated at a temperature of F. Zinc panels from the bath using 20 a. s. f. (amperes per square foot) plating current. The zinc plated panels were given a bright dip in 0.5% nitric acid. The zinc plated panels so produced had a bright lustrous finish.

Example II Sodium hydroxide I::IIIIIIIIIII: 10.5 Sodium polysulfide 0.05 Silver 0.005 This bath was operated at a temperature of 90 F. Zinc was plated on cathode panels from the bath using 20 ASP at the cathode. The zinc plated panels were given a bright dip in 0.5% nitric acid. With the use of the sodium polysulfide purifying agent, the zinc plated panels produced had a mirror bright finish.

It is intended that all matter contained in the above specification shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. In an alkaline cyanide zinc electroplating electrolyte for depositing substantially pure zinc which comprises as its essential ingredients zinc cyanide in an amount of about 8 to 10 ounces per gallon, sodium cyanide, and caustic soda, silver as a brightening agent admixed in the electrolyte in an amount of from 0.0005 to 0.5 ounce per gallon of electrolyte.

2. In an alkaline cyanide Zinc electroplating electrolyte for depositing substantially pure zinc which comprises as its essential ingredients zinc cyanide in an amount of about 8 to 10 ounces per gallon, sodium cyanide, caustic soda, and at least one purifying agent selected from the group consisting of sodium sulfide and sodium polysulfide admixed in the electrolyte, silver as a brightening agent admixed in the electrolyte in an amount of from 0.0005 to 0.02 ounce per gallon of electrolyte.

3. In the process of plating zinc on a base with an alkaline cyanide Zinc electroplating electrolyte comprising as its essential ingredients zinc cyanide in an amount of about 8 to 10 ounces per gallon, sodium cyanide, and caustic soda, the steps comprising adding silver to the electrolyte in an amount of from 0.0010 to 0.01 ounce per gallon of electrolyte and then passing an electrical current from an anodeflthrough the electrolyte and to the base to deposit substantially pure zinc on the base.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN ALKALINE CYANIDE ZINC ELECTROPLATING ELECTROLYTE FOR DEPOSITING SUBSTANTIALLY PURE ZINC WHICH COMPRISES AS ITS ESSENTIALLY INGREDIENTS ZINC CYANIDE IN AN AMOUNT OF ABOUT 8 TO 10 OUNCES PER GALLON, SODIUM CYANIDE, AND CAUSTIC SODA, SILVER AS A BRIGHTENING AGENT ADMIXED IN THE ELECTROLYTE IN AN AMOUNT OF FROM 0.0005 TO 0.5 OUNCE PER GALLON OF ELECTROLYTE. 